On Thu, May 27, 2010 at 10:13:12AM -1000, Zachary Amsden wrote: > On 05/27/2010 06:02 AM, Glauber Costa wrote: > >On Thu, May 27, 2010 at 11:15:43AM +0300, Avi Kivity wrote: > >>On 05/26/2010 09:04 PM, Glauber Costa wrote: > >>>This patch adds a file that documents the usage of KVM-specific > >>>MSRs. > >>> > >>Looks good. A few comments: > >> > >>>+ > >>>+Custom MSR list > >>>+-------- > >>>+ > >>>+The current supported Custom MSR list is: > >>>+ > >>>+MSR_KVM_WALL_CLOCK: 0x11 > >>>+ > >>>+ data: physical address of a memory area. > >>Which must be in guest RAM (i.e., don't point it somewhere random > >>and expect the hypervisor to allocate it for you). > >> > >>Must be aligned to 4 bytes (we don't enforce it though). > >I don't see the reason for it. > > > >If this is a requirement, our own implementation > >is failing to meet it. > > It's so the atomic write actually is atomic. Which atomic write? This is the wallclock, we do no atomic writes for querying it. Not to confuse with system time (the other msr). > Stating a 4 -byte > alignment requirement prevents the wall clock from crossing a page > boundary. Yes, but why require it? reading the wallclock is not a hot path for anybody, is usually done just once, and crossing a page boundary here does not pose any correctness issue. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
